A variety of wafer holder structures for use in semiconductor manufacturing apparatuses have been proposed to date. For example, Japanese Examined Pat. App. Pub. No. H06-28258 proposes a semiconductor wafer-heating device including: a heater part made of ceramic, in which a resistive heating element is embedded, and that is provided with a wafer-heating side and is installed within a reaction chamber; a columnar support part provided on the side of the heater part other than its wafer-heating side and that forms a hermetic seal between it and the reaction chamber, and electrodes connected to the resistive heating element and leading out to the reaction chamber exterior so as substantially not to be exposed to the reaction-chamber interior space.
In another example, Japanese Pat. Pub. No. 2525974 proposes a structure in which tubular pieces are joined to a ceramic susceptor part (wafer holder). Specifically, proposed therein is a semiconductor wafer heating device including a ceramic susceptor part, a retaining part, installed in a reaction chamber, for supporting the ceramic susceptor part, and leads connected to heater terminals. At least one of the leads is surrounded by a tubular piece made of an inorganic insulating material, and one end of the tubular piece is joined hermetically onto the ceramic susceptor, while the other end thereof is inserted through a through-hole provided in the reaction chamber, where it is sealed hermetically.
With the transition to silicon wafers of larger diametric span moving forward in recent years uniform temperature distribution over the wafer support surface is in particular demanded of wafer holders. A drawback with the apparatus set out in Japanese Examined Pat. App. Pub. No. H 6-28258, however, is that, because the ceramic susceptor, being a wafer holder, is supported by a columnar support part that is hermetically sealed between it and the reaction chamber and that is in contact with the ambient air outside the reaction chamber, the temperature uniformity of the wafer support surface is compromised due to heat radiation toward the ambient air.
Likewise, in the structure set out in the above-mentioned Japanese Pat. Pub. No. 2525974, the tubular piece that houses the lead is joined to the ceramic susceptor part and passes through the reaction chamber, where the chamber is sealed off hermetically; therefore, the interior of the tubular piece will inevitably be at the atmospheric pressure, whereas the wafer-processing atmosphere within the reaction chamber is at reduced pressure or a vacuum. The consequent problem has been that the amount of heat that dissipates through the air at atmospheric pressure within the tubular piece grows greater than that elsewhere, reducing the temperature at the joint of the ceramic susceptor part with the tubular piece and spoiling the temperature uniformity of the wafer support surface. Moreover, the fact that the tubular piece is joined to the ceramic susceptor has meant that the escape of heat from the joint portion is significant, which has meant that the temperature uniformity of the wafer support surface is further compromised as a result.
What is more, the lead for supplying power to the ceramic susceptor part is exposed to the ambient air and toward the ceramic susceptor part its temperature grows due to the heating of the ceramic susceptor part. The problem has therefore been that the portion of the lead that has become temperature-elevated is more likely to corrode due to oxygen in the air. Another problem that has persisted has been that because the tubular piece is joined to the ceramic susceptor part and the interval between it and the reaction chamber is hermetically sealed costs rise owing to the low throughput in the joining.